British Prime Minister Theresa May on Sunday said she could sack Foreign Secretary Boris Johnson, as she tries to reassert her authority after a series of political disasters, The Sunday Times reported.

The newspaper asked May about her plans for Johnson, who is accused by some of the prime minister’s allies of undermining her by putting forward his own vision for Britain’s exit from the European Union.

“It has never been my style to hide from a challenge and I’m not going to start now,” it quoted May as saying. “I’m the prime minister, and part of my job is to make sure I always have the best people in my Cabinet, to make the most of the wealth of talent available to me in the party.”

May’s authority over her Conservative Party has been shaky ever since she called a snap election in June, in which she lost her majority in Parliament. Her comments are part of efforts to get on the front foot as leaders return to Parliament this week, after a damaging conference season, The Guardian reported.

Johnson, seen as a potential successor to May, said Conservative lawmakers pushing to unseat her were “nutters”. He added that a change would lead to demands for another election, which could bring a resurgent Labour Party back to power, Reuters reported.

The speculation about May’s position comes ahead of crucial Brexit talks between Britain and the European Union. The political uncertainty has led to concerns that there will be no deal by March 2019, when the United Kingdom leaves the bloc.